This invention relates to tube expanders of the type used for step by step expansion of tubes into tube support sheets, and in particular, to a novel indexing device for achieving the step by step expansion.
Mechanical expansion of tubes into a tube support sheet is a well-known art and is accomplished through the use of a tool known as an expander. Generally, tube expanders include a tapered mandrel, axially movable within a support cage. Movement of the mandrel results in rollers, mounted within the cage being forced into contact with the inner surface of the tube to mechanically expand the tube. The expansion of the tubes to achieve a mechanical bond between the outer surface of the tube and the surrounding surface of the tube support sheet must be extremely accurate to prevent leaks from occurring between the contacting surfaces. In addition, if the mechanical bond is not properly achieved, any vibrations might cause relative movement between the tube and support sheet whereby a tube failure may result due to the rubbing action of the tube support sheet on the tube.
In some applications, as for example nuclear reactors, the tube support sheet is extremely thick as for example, such tube support sheet may have a thickness of 11 inches to 22 inches. In order to achieve the expansion of the tube along its entire axial surface into the surrounding tube support sheet, step tube expanders have been developed. Essentially, a step tube expander includes a mandrel disposed within a cage. The cage generally includes a plurality of circumferential grooves axially spaced thereabout. The distance between such axial grooves are generally somewhat less than the length of the rollers used in the tube expander. The cage is suitably advanced relative to the support sheet from one axial groove to the next to achieve the step by step expansion of the tube within the tube support sheet.
Heretofore, the indexing means employed to achieve the step by step advance of the cage has either been relatively expensive, or unreliable and time consuming. Inaccuracies have resulted through the use of indexing devices which require manual manipulation whereby it has been possible for an operator to skip an expansion step resulting in an improperly expanded tube. In addition, a significant amount of time has been lost as a result of the need to manually move the indexing device. Accordingly, it is a primary object of the invention to provide a simple and accurate automatic indexing device to achieve the step by step movement of the cage of an expander.